Reptiles and Birds

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Vertebrates, Ch 34, U314PP
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Well which DID come first?
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• Concept 34.6 Amniotes are tetrapods that have a
  terrestrially adapted egg
• Amniotes are a group of tetrapods
• Whose living members are the reptiles, including
  birds, and the mammals

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• A phylogeny of amniotes

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Derived Characters of Amniotes

• Amniotes are named for the major derived
  character of the clade, the amniotic egg
• Which contains specialized membranes that protect
  the embryo

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• The extraembryonic membranes
• Have various functions

a private pond
Can be hard-shelled (birds) or soft and leathery
(reptiles)
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• Amniotes also have other terrestrial adaptations
• relatively impermeable skin (the protein keratin
  in most reptiles crocodiles have scutes- more
  permeable scales since they live in water)
• thoracic breathing ventilate the lungs
• Leg positioning under body greater mobility than
  amphibians
• Internal fertilization
• Circulation- nearly complete four-chambered heart
  (most reptiles) or complete four-chambered heart
  (birds)
• ectothermic (some, most? reptiles) endothermic
  (birds)
• Note- old terms cold blooded and warm blooded

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• Most reptiles are ectothermic
• Absorbing external heat as the main source of
  body heat
• Birds are endothermic
• Capable of keeping the body warm through
  metabolism

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Early Amniotes

• Early amniotes
• Appeared in the Carboniferous period
• Included large herbivores and predators

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Reptiles

• The reptile clade includes
• The tuatara, lizards, snakes, turtles,
  crocodilians, birds, and the extinct dinosaurs

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• Reptiles
• Have scales that create a waterproof barrier
• Lay shelled eggs on land

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The Origin and Evolutionary Radiation of Reptiles

• The oldest reptilian fossils
• Date to about 300 million years ago
• The first major group of reptiles to emerge
• Were the parareptiles, which were mostly large,
  stocky herbivores

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• As parareptiles were dwindling (due to predation
  by the anscestors to the mammals)
• The diapsids were diversifying
• The diapsids are composed of two main lineages
• The lepidosaurs and the archosaurs

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• The dinosaurs
• Diversified into a vast range of shapes and sizes
  from the archosaur lineage
• Includes the theropods (T. rex)

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• Traditionally, dinosaurs were considered slow,
  sluggish creatures
• But fossil discoveries and research have led to
  the conclusion that dinosaurs were agile and fast
  moving
• Endothermic? Ectothermic? Yes to both!
• Paleontologists have also discovered signs of
  parental care among dinosaurs

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The dinosaur demise

• Dinosaur extinction rates had accelerated prior
  to massive extinction event
• Events that led to final extinction?
• Global climate change
• Change in sea level
• Competition with mammals (minor)
• Dietary changes with emerging angiosperms?
• Other ideas?

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Most smaller animals survived the extinction
event paved the way for diversification
Lets be fair reptiles survived the extinction
event too more reptile species than mammal
species around today
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Lepidosaurs

• One surviving lineage of lepidosaurs
• Is represented by two species of lizard-like
  reptiles called tuatara

Possess a 3rd, covered eye may help in detecting
overheating
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• The other major living lineage of lepidosaurs
• Are the squamates, the lizards and snakes
• Lizards
• Are the most numerous and diverse reptiles, apart
  from birds ?

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• Snakes are legless lepidosaurs
• That evolved from lizards

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Turtles

• Turtles
• Are the most distinctive group of reptiles alive
  today
• Some turtles have adapted to deserts
• And others live entirely in ponds and rivers

Evolution of turtles unclear did that come from
early parareptiles? Not sure
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• All turtles have a boxlike shell
• Made of upper and lower shields that are fused to
  the vertebrae, clavicles, and ribs

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Alligators and Crocodiles

• Crocodilians
• Belong to an archosaur lineage that dates back to
  the late Triassic

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Birds

• Birds are archosaurs
• But almost every feature of their reptilian
  anatomy has undergone modification in their
  adaptation to flight
• (Since they are archosaurs, like crocodiles, it
  is not surprising they show up so closely in the
  beta hemoglobin analysis, is it?)
• Arose from some bipedal theropod (dinosaur group)
  that must have been endothermic
• A recent study suggests that birds arose as an
  identifiable group before the extinction and
  survived it (as opposed to having diversified
  from an ancestor after the extinction, as was
  previously thought)

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Derived Characters of Birds

• If the are basically reptiles, why the class
  designation Aves?
• Many of the characters of birds
• Are adaptations that facilitate flight
• Multiple orders one (Passeriformes) includes 60
  of all species
• Song birds (well-developed vocal organs, perching
  feet)

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• A birds most obvious adaptations for flight
• Are its wings and feathers

Provide lift, conserve heat Maximum flexibility
with minimum weight

• Others?
• No urinary bladder
• Females only have one ovary
• Small gonads except during mating season
• Toothless
• Light skeleton

Air has only been conquered by four groups of
animals name them!
Birds, bats, insects, some dinosaurs
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The Origin of Birds

• Birds probably descended from theropods
• A group of small, carnivorous dinosaurs

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• By 150 million years ago
• Feathered theropods had evolved into birds
• Archaeopteryx
• Remains the oldest bird known

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Living Birds

• The ratites, order Struthioniformes
• Are all flightless

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• The demands of flight
• Have rendered the general body form of many
  flying birds similar to one another

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Flight expensive metabolically

• Efficient respiration (more efficient than
  mammals)
• Efficient circulation
• Birds that fly- 600-1000 bpm
• Flightless? (ostrich- 70 bpm)
• Endothermy

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• Foot structure in bird feet
• Shows considerable variation